Abstract
We characterize the influence of the ionic ratio on the dynamic self-assembly process involving a macrocyclic tetraimidazolium molecular box and small dianionic salts into highly defined, colloid-like ionic clusters in solution, called ionoids. Based on our studies utilizing dynamic light scattering (DLS) and continuous wave electron paramagnetic resonance (CW EPR) spectroscopy, we determine a region of privileged ionic ratios, which allow the formation of monodisperse, spheroidal structures of loosely bound ions in solution with adjustable (i) hydrodynamic radii between 6 nm and 12 nm and (ii) shape anisotropy. Inspired by Hertzsprung-Russell diagrams (HRDs) used in astrophysics to describe the fate of stars, we construct ionoid evolution diagrams (IEDs). IEDs are essential for grasping and describing the highly complex temporal development of these dynamically self-assembled structures in solution from the level of the individual ionic building blocks to stable clusters with a minimum lifetime of months, and thus aid in crafting future globular ionoids and anisotropic ionic clusters.
Highlights
Soft condensed matter comprises classes of materials like colloids, polymers, liquid crystals, amphiphiles, micelles and polyelectrolytes,[1,2] not to mention the whole field of biological soft matter.[3,4] These systems usually have structural length scales from one to several hundred nanometers and fall within the domain of ‘nanostructured materials’.1,5In recent publications,[6,7] we characterized the formation of loosely bound ion-based colloid-like globular clusters of several nanometer size, termed globular ionoids
Note that we can employ continuous wave electron paramagnetic resonance (CW electron paramagnetic resonance (EPR)) spectroscopy only for measuring the ion cloud state that forms in the initial hours after system preparation
As previously established,[6,7] we used dynamic light scattering (DLS) to directly observe the development of ionic clusters, mainly through their scattering profiles and the derived hydrodynamic radius
Summary
In recent publications,[6,7] we characterized the formation of loosely bound ion-based colloid-like globular clusters of several nanometer size, termed globular ionoids. These structures, whose fabrication is based on the process of ionic self-assembly (ISA),[8] represent a novel subclass inside the major field of supramolecular chemistry.[9,10,11] Supramolecular chemistry in general aspires to the development of highly complex chemical systems from components interacting through noncovalent intermolecular forces. The ISA process involves (i) electrostatic interactions as the primary driving force[12] and (ii) weaker noncovalent interactions (such as solvation, hydrogen bonding, van der Waals etc.) as the secondary driving force.[13]
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